TireGeoCalcTire Size Calculator
Enter an original tire size and a new tire size to compare their geometry: overall diameter, circumference, revolutions per mile/km, speedometer error at common speeds, and the change in ground clearance and width. Everything is computed in your browser from the size you type. No account, no vehicle lookup, no personal data collected.
Compare two tire sizes
| Width | Sidewall | Rim | Diameter | Circumference | Rev/mile | Rev/km |
|---|
Speedometer: indicated vs. actual
| Indicated | Actual |
|---|
This tool computes geometry from the tire size text entered only. It does not know your vehicle, does not inspect your tires, and does not look up manufacturer specifications.
The calculator results are based on the mathematical equations of the tire sizes entered, not a guarantee of fitment. Diameter difference under the common 3% guideline is not a fitment guarantee. Modifying tire size can affect suspension, brake caliper and body clearance, speedometer accuracy, and ABS/ESC calibration. Always check your vehicle's owner manual, the tire placard on the driver's door jamb, and consult a qualified installer before purchase.
How we calculate: formulas, rounding and reference sources.